1. Field of the Invention
The present invention relates to workstations in general and, in particular, to multi-media workstations in which full motion video images and computer generated information (graphic and non-graphic) are shown on displays.
2. Prior Art
The proliferation of multi-media workstations create the need for new techniques and/or devices to process multi-media information. Generally, the multi-media workstation is capable of processing electrical signals representative of voice, data and video information. As a general proposition, the different types of information (i.e., data, voice or video) are propagated on a common transmission medium.
A conventional workstation is comprised of a controller which is usually a personal computer (PC) and one or more Input/Output (I/O) devices. The I/O devices may include printers, displays, etc. Probably, the display unit is the most important of all the I/O devices. It gives a user a visual image of information inputted into the system and results based upon queries from the user. A conventional device, commonly known as a video adapter, couples the display device to the bus of the PC. An operating system such as OS/2.sup.R is executed on the PC and provides the necessary facilities (e.g., interfaces, protocols, format, etc.) for providing information on the display via the video adapter. The OS/2.sup.R product partitions the display screen into separate areas or windows in which selected information can be inserted and displayed to the user.
It is desirable for multi-media applications to display full motion video simultaneously with conventional computer graphic information in a windowing environment. Many primary sources of full motion video are in a format known as National Television Standards Committee (NTSC). An NTSC video image is composed of successive frames. Each frame consists of an interlaced odd and even field. Each field has 262.5 scan lines, 240 of which contain video information. Therefore, each frame has 480 interlaced lines of video information.
To integrate the 480 lines of video information with computer graphics in a windowing environment, requires scaling the video image into a size which fits into a window of user defined height. In addition to scaling, the interlaced image has to be de-interlaced in order to be displayed in the window environment.
One known scaling technique is decimination. In this technique, information is decimated (discarded) on a field basis, providing a maximum of 240 scaled window heights. When information is decimated on a field basis, both the even and the odd field are treated alike, save for a possible offset between the two, and the same number of lines of video information are discarded from each field. Field based scaling via decimation is likely to introduce decimation artifacts. The decimation artifacts reduce the output image quality when key visual cues in the input image are fully discarded in the scaled output image.
U. S. Pat. No. 4,947,257 describes a system for combining a plurality of video signals with still imagery such as text or graphics for display on a high definition (HD) TV. The video signals are scaled in order to fit into particular windows of a display screen. The scaling is done by a processor executing a vertical and horizontal cubic spine interpolation algorithm.